Methods and devices for fill state measurement that work according to the plumb-bob principle are sufficiently known. For example, in the documents, German patents, DE 21 51 094, DE 24 01 486 B2, DE-PS 819 923, and DE 39 42 239 A1; US-PS 3,838,518; German patents, DE 195 43 352 A1, G 70 31 884.2, DE-PS 819 923, and G 73 29 766.2, DE 19730196 A1, and DE 28 53 360 A1, fill state measuring systems for highly precise fill state determination are described, which work according to the plumb-bob principle. In these methods for the fill state measurement according to the plumb-bob principle, a plumb bob hanging on a measuring rope is lowered onto the filling material or bulk material. Upon reaching the filling material, the length of the measuring rope that was taken off the rope drum is determined, and the fill height or fill quantity is displayed on a display device. Different plumb bobs are advantageously used for different filling materials.
The main field of application of electromechanical bob plumbing is the fill state measurement of very tall containers, where solutions with other measuring principles are very cost-intensive or not possible for physical reasons. With electromechanical bob plumbing, fill states in containers of, at present, up to approx. 70 m height can be measured with a precision of less than one millimeter.
Other devices for fluid level measurement and density determination, which function according to the displacement measuring principle, became known from German patents, DE 37 21164 A1, DE2853360A1, DE 2401486 B2, and DE 2659416 A1.
From German patent, DE2853360A1 is known a fluid level measuring device with a displacement body. This displacement body is provided with a wire, which can be wound onto or unwound from a drum. The drum is driven by a shaft by means of a motor, wherein a device for determining the change in the torque exerted on the shaft is provided.
In German patent, DE 2659416 A1, a device for measuring a fluid level is described, in which the change in the fluid level is converted into a rotational movement. Furthermore, a magnetic head is provided on an arm, which rotates according to the change in the fluid level and, in the process, senses magnetic fields, which are produced by electrical conductors arranged on the circumference of a disk.
German patent, DE 2401486 B2 discloses a fill state display device according to the displacement measuring principle, in which a rope is unwound from or wound onto a drum, wherein a counting disk co-rotates and, in the process, generates via shielding-gas contact switches a continuous pulse sequence, which is a measurement of the rope length used.
Published international application, WO2012/040017 A2 describes a method for checking an electromechanical fill state measuring device, in which the torque is determined in a test mode by means of the measuring drum, and a mechanical problem is found if the measured torque exceeds a specified upper value or if the measured torque falls below a specified lower value. The test mode is initiated and executed between two measurements in the measurement mode, so that the measurement operation must be interrupted in this method. In this method, it is furthermore disadvantageous that the test mode requires a long test time, during which no measurement results are delivered.
From German patent, DE 37 21164 A1, a fill state measuring device is known, which includes a float on a wire, which floats on the surface of a fluid (not shown). The wire is wound on a drum and can be spooled onto this drum or unspooled from it. The bottom of the drum is connected to a measuring shaft. If the fluid level, on which the float floats, changes, the stress exerted by the wire on the drum thus also changes. This change in the stress exerted by the wire is converted into a torque on the measuring shaft via an outer magnetic ring acting as a coupling part. The cylindrical outer magnetic ring is connected to the bottom inside the drum. Magnetic poles, south poles and north poles, are arranged alternately in the circumferential direction of the outer magnetic ring. On the inner magnetic ring connected to the measuring shaft, magnetic north and south poles are alternately formed in the same quantity as on the outer magnetic ring. An electromagnetic transducer, e.g., a Hall element, is arranged on the outer circumference of the inner magnetic ring in the border area between different magnetic poles. If a force that causes a relative movement between the outer and inner magnetic rings is generated during a change in the fluid level to be measured, a change in the magnetic flux present between the outer and the inner magnetic rings causes an electrical signal in the electromagnetic transducer, by means of which signal the measuring shaft is rotated such that the relative movement between the inner and the outer magnetic rings is returned to zero, and a measured value of the fluid level reached is obtained thereby. By means of a sliding contact located on the measuring shaft, the electrical signal of the electromagnetic transducer is transmitted in the inner drum to the servomotor control. This mechanical tapping has the disadvantage that it does not take place without wear.